Reference electrode having a microfluidic flowing liquid junction

Abstract

A flowing junction reference electrode comprises a microfluidic liquid junction member situated between a pressurized reference electrolyte solution and a sample solution. The liquid junction member has an array of nanochannels spanning the member and physically connecting the electrolyte and the sample. The number of nanochannels in the array can be between 10 and 10 8 . Preferably, the nanochannels are substantially straight and parallel to one another. The nanochannels can be coated to facilitate the flow of the electrolyte solution through the junction member. The nanochannels can have widths of between 1 and 500 nanometers, and the width of any one nanochannel is substantially equal to the width of any other nanochannel. The member can be manufactured out a polymer such as polycarbonate and polyimide, and may also be made of silicon, glass, or ceramic. In one embodiment, the reference electrode includes means for pressurizing the electrolyte solution.

1. A method of manufacturing a flowing junction reference electrode, the method comprising:
 providing a chamber for receiving a reference electrolyte solution, wherein the chamber is configured to allow pressurization of the electrolyte solution; and 
 providing a liquid junction member having N discrete nanochannels, the nanochannels having diameters D and lengths L, wherein the nanochannels are substantially straight and substantially parallel to one another, wherein N is less than approximately 100,000, and wherein the member is in fluid communication with the electrolyte solution; 
 filling said chamber with said reference electrolyte solution, said reference electrolyte solution having a viscosity η; 
 pressurizing the electrolyte solution to a pressure P E ; 
 configuring the reference electrode such that the liquid junction member can be brought into fluid communication with a sample solution such that the junction member is situated between the electrolyte solution and the sample solution; and 
 selecting ΔP, D,η, and L such that 
 
     
       
         
           
             
               
                 D 
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               Δ 
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               P 
             
             
               32 
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               η 
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               L 
             
           
         
       
       is greater than about 0.1 centimeter per second, wherein ΔP is a pressure differential between P E  and a pressure P S  of the sample solution, and wherein ΔP is greater than approximately 10 psi and less than approximately 100 psi. 
     
   
   
     2. The method of  claim 1 , wherein N is less than approximately 50,000. 
   
   
     3. The method of  claim 1 , wherein N is less than approximately 10,000. 
   
   
     4. The method of  claim 1 , wherein N is less than approximately 1,000. 
   
   
     5. The method of  claim 1 , wherein N is greater than approximately 10. 
   
   
     6. The method of  claim 1 , wherein N is greater than approximately 100. 
   
   
     7. The method of  claim 1 , wherein a diameter D i  of any one nanochannel is substantially equal to a diameter D j  of any other nanochannel. 
   
   
     8. The method of  claim 1 , wherein D is greater than approximately 1 nanometer and less than approximately 900 nanometers. 
   
   
     9. The method of  claim 1 , wherein D is greater than approximately 5 nanometers and less than approximately 750 nanometers. 
   
   
     10. The method of  claim 1 , wherein D is greater than approximately 10 nanometers and less than approximately 500 nanometers. 
   
   
     11. The method of  claim 1 , wherein D is greater than approximately 40 nanometers and less than approximately 250 nanometers. 
   
   
     12. A method of manufacturing a flowing junction reference electrode, the method comprising:
 providing a chamber for receiving a reference electrolyte solution, wherein the chamber is configured to allow pressurization of the electrolyte solution; and 
 providing a liquid junction member having N discrete nanochannels, the nanochannels having diameters D and lengths L, wherein N is less than approximately 100,000, wherein the member is in fluid communication with the electrolyte solution, and wherein the nanochannels are coated with a hydrophilic material. 
 
   
   
     13. A method of manufacturing a flowing junction reference electrode, the method comprising:
 providing a chamber for receiving a reference electrolyte solution, wherein the chamber is configured to allow pressurization of the electrolyte solution; and 
 providing a liquid junction member having N discrete nanochannels, the nanochannels having diameters D and lengths L, wherein N is less than approximately 100,000, wherein the member is in fluid communication with the electrolyte solution, and wherein the nanochannels are coated with a hydrophobic material. 
 
   
   
     14. A method of manufacturing a flowing junction reference electrode, the method comprising:
 providing a chamber for receiving a reference electrolyte solution, wherein the chamber is configured to allow pressurization of the electrolyte solution; and 
 providing a liquid junction member having N discrete nanochannels, the nanochannels having diameters D and lengths L, wherein N is less than approximately 100,000, wherein the member is in fluid communication with the electrolyte solution, and wherein the junction member is manufactured as a single planar element. 
 
   
   
     15. A method of manufacturing a flowing junction reference electrode, the method comprising:
 providing a chamber for receiving a reference electrolyte solution, wherein the chamber is configured to allow pressurization of the electrolyte solution; and 
 providing a liquid junction member having N discrete nanochannels, the nanochannels having diameters D and lengths L, wherein N is less than approximately 100,000, wherein the member is in fluid communication with the electrolyte solution, and wherein the junction member comprises a planar element of microchannels coupled to a planar element of nanochannels. 
 
   
   
     16. The method of  claim 15 , wherein the planar element of microchannels is bonded to the planar element of nanochannels. 
   
   
     17. The method of  claim 15 , wherein the planar element of the microchannels is thermally or adhesively bonded to the planar element. 
   
   
     18. The method of  claim 15 , wherein the microchannels have widths greater than approximately 5 micrometers and less than approximately 25 micrometers. 
   
   
     19. A method of manufacturing a flowing junction reference electrode, the method comprising:
 providing a chamber for receiving a reference electrolyte solution, wherein the chamber is configured to allow pressurization of the electrolyte solution; and 
 providing a liquid junction member made of a polymer and having N discrete nanochannels, the nanochannels having diameters D and lengths L, wherein N is less than approximately 100,000, and wherein the member is in fluid communication with the electrolyte solution; 
 filling said chamber with said reference electrolyte solution, said reference electrolyte solution having a viscosity η; 
 pressurizing the electrolyte solution to a pressure P E ; 
 configuring the reference electrode such that the liquid junction member can be brought into fluid communication with a sample solution such that the junction member is situated between the electrolyte solution and the sample solution; and 
 selecting ΔP, D, η, and L such that 
 
     
       
         
           
             
               
                 D 
                 2 
               
               ⁢ 
               Δ 
               ⁢ 
               
                   
               
               ⁢ 
               P 
             
             
               32 
               ⁢ 
               η 
               ⁢ 
               
                   
               
               ⁢ 
               L 
             
           
         
       
       is greater than about 0.1 centimeter per second, wherein ΔP is a pressure differential between P E  and a pressure P S  of the sample solution, and wherein ΔP is greater than approximately 10 psi and less than approximately 100 psi. 
     
   
   
     20. The method of  claim 19 , wherein the polymer is selected from the group consisting of polycarbonate, polyethylene, and polyimide. 
   
   
     21. A method of manufacturing a flowing junction reference electrode, the method comprising:
 providing a chamber for receiving a reference electrolyte solution, wherein the chamber is configured to allow pressurization of the electrolyte solution; and 
 providing a liquid junction member made of silicon, glass, or ceramic, and having N discrete nanochannels, the nanochannels having diameters D and lengths L, wherein N is less than approximately 100,000, and wherein the member is in fluid communication with the electrolyte solution; 
 filling said chamber with said reference electrolyte solution, said reference electrolyte solution having a viscosity η; 
 pressurizing the electrolyte solution to a pressure P E ; 
 configuring the reference electrode such that the liquid junction member can be brought into fluid communication with a sample solution such that the junction member is situated between the electrolyte solution and the sample solution; and 
 selecting ΔP, D, η, and L such that 
 
     
       
         
           
             
               
                 D 
                 2 
               
               ⁢ 
               Δ 
               ⁢ 
               
                   
               
               ⁢ 
               P 
             
             
               32 
               ⁢ 
               η 
               ⁢ 
               
                   
               
               ⁢ 
               L 
             
           
         
       
       is greater than about 0.1 centimeter per second, wherein ΔP is a pressure differential between P E  and a pressure P S  of the sample solution, and wherein ΔP is greater than approximately 10 psi and less than approximately 100 psi. 
     
   
   
     22. A method of manufacturing a flowing junction reference electrode, the method comprising:
 providing a chamber for receiving a reference electrolyte solution, wherein the chamber is configured to allow pressurization of the electrolyte solution; and 
 providing a liquid junction member having N discrete nanochannels, the nanochannels having diameters D and lengths L, wherein N is less than approximately 100,000, and wherein the member is in fluid communication with the electrolyte solution; 
 filling said chamber with said reference electrolyte solution, said reference electrolyte solution having a viscosity η; 
 providing means for pressurizing the electrolyte solution; 
 pressurizing the electrolyte solution to a pressure P E ; 
 configuring the reference electrode such that the liquid junction member can be brought into fluid communication with a sample solution such that the junction member is situated between the electrolyte solution and the sample solution; and 
 selecting ΔP, D, η, and L such that 
 
     
       
         
           
             
               
                 D 
                 2 
               
               ⁢ 
               Δ 
               ⁢ 
               
                   
               
               ⁢ 
               P 
             
             
               32 
               ⁢ 
               η 
               ⁢ 
               
                   
               
               ⁢ 
               L 
             
           
         
       
       is greater than about 0.1 centimeter per second, wherein ΔP is a pressure differential between P E  and a pressure P S  of the sample solution, and wherein ΔP is greater than approximately 10 psi and less than approximately 100 psi. 
     
   
   
     23. The method of  claim 22 , wherein the means for pressurizing is selected from the group consisting of a pressurized collapsible bladder, an electro-osmotic pump, a mechanical pump, a piezo-electric pump, and a electro-hydrodynamic pump. 
   
   
     24. A method of manufacturing a flowing junction reference electrode, the method comprising:
 providing a chamber for receiving a reference electrolyte solution, wherein the chamber is configured to allow pressurization of the electrolyte solution; and 
 providing a liquid junction member having N discrete nanochannels, the nanochannels having diameters D and lengths L, wherein N is less than approximately 100,000, and wherein the member is in fluid communication with the electrolyte solution; 
 filling said chamber with said reference electrolyte solution, said reference electrolyte solution having a viscosity η; 
 pressurizing the electrolyte solution to a pressure P E ; 
 configuring the reference electrode such that the liquid junction member can be brought into fluid communication with a sample solution such that the junction member is situated between the electrolyte solution and the sample solution; 
 selecting ΔP, D, η, and L such that 
 
     
       
         
           
             
               
                 D 
                 2 
               
               ⁢ 
               Δ 
               ⁢ 
               
                   
               
               ⁢ 
               P 
             
             
               32 
               ⁢ 
               η 
               ⁢ 
               
                   
               
               ⁢ 
               L 
             
           
         
       
       is greater than about 0.1 centimeter per second, wherein ΔP is a pressure differential between P E  and a pressure P S  of the sample solution, and wherein ΔP is greater than approximately 10 psi and less than approximately 100 psi; and 
       providing a sensing electrode. 
     
   
   
     25. The method of  claim 24 , wherein the sensing electrode is selected from the group consisting of pH electrodes, other ion-selective electrodes, and redox electrodes.